Well actually....
...not quite.
While it's true you'll lose a generation, the loss will be far less than you'd lose making a copy of the cassette final mix onto another cassette.
So the advantage is a much cleaner 3rd generation than a cassette's 2nd generation. Kind of along the same principle of digital track bouncing thru the converters. You can bounce an ADAT's track thru analog many, many times before you even start to notice any audible degradation. You'd be lucky to be able to do even one bounce on an analog Portastudio before you hear a loss.
Bruce